/Engine/Plugins/Media/ImgMedia/Source/ImgMedia/Public/ImgMediaSource.h
Returns true if InPath is under InBasePath. If so, fills out OutRelativePath with the relative path between them
static bool IsPathUnderBasePath ( const [FString](API\Runtime\Core\Containers\FString) & InPath, const [FString](API\Runtime\Core\Containers\FString) & InBasePath, [FString](API\Runtime\Core\Containers\FString) & OutRelativePath )